1. Field of the Invention
This invention relates to a method and apparatus for locking a threaded joint. More specifically, the invention relates to a resilient holding device for a threaded joint or coupling that, for purposes of disassembly, requires the application of a torque that is in excess of the torque required to assemble or tighten the joint or coupling.
2. Description of the Prior Art
Various methods and apparatus have been proposed and used in the past to temporarily lock a threaded joint or coupling in place. Thus, it is known that to secure, for example, a nut on a bolt, several types of devices can be employed such as a pair of nuts under tension, a Castle nut and cotter pin, a split nut and closing screw, various types of lock washers and lock nuts or even selected chemicals. Each of these methods exhibit certain advantages and disadvantages. Yet none are known to Appllicant to have the ability to be easily assembled with a first magnitude of torque and then require a second torque of several multiples of magnitude greater to disassemble, wherein the apparatus is usable immediately after assembly and is reusable a large number of times. Such a torque biased locking device is advantageous in many useful applications.
Various prior art references have suggested methods which take advantage of a looped spring's ability to change diameter. For example in U.S. Pat. Nos. 2,846,240 and 3,532,101 a coiled spring looped back on itself forming a closed ring is used as a detent in a concentrically sleeved non-threaded coupling thus forming an essentially snap together and quick-release connection. Similarly in U.S. Pat. No. 2,848,135 a spring snaps through a series of semi-circular grooved threads on the inner member of the coupling unit. Other devices that are similar to these, in that the looped spring makes a transition in diameter during assembly and disassembly, are known, such as in the pipe coupling of U.S. Pat. No. 2,921,801, as in the grip elements in the quick-release coupling of U.S. Pat. Nos. 2,922,665 and 2,939,728, in the well tool locking device of U.S. Pat. No. 3,250,331, and in the inflatable clamping means of U.S. Pat. No. 3,420,554.
In U.S. Pat. No. 1,814,478 a connector fitting is disclosed employing a spring filled with a deformable material. The filled spring is wrapped around a threadless conduit and acts as a gripping device and seal for coupling the threadless conduit to a conduit fitting. In U.S. Pat. No. 3,218,095 a sealing ring having an internal spring is employed in a tube coupling. In U.S. Pat. No. 1,882,520 a spiral spring is used for locking two concentric non-threaded pieces of a reciprocating pneumatic tool by providing an internal annulus with external opening through which the spring is inserted and removed each time the apparatus is to be disassembled. In U.S. Pat. No. 3,065,005 a casing stop collar is disclosed that utilizes a spring in a similar manner. And in U.S. Pat. No. 3,712,647 various combinations of spring structures with deformable seals are combined in a compression pipe connection.
Springs have also been used in threaded couplings for other purposes. For example, in U.S. Pat. No. 3,104,583 a flexing resilient threaded closure is disclosed wherein a spring is installed in a semi-circular helical groove and thus serves as one of the threaded surfaces. Such a closure is useful in autoclave vessels to better distribute stress associated with high temperature, high pressure cyclic operations. But none of the suggested uses of the looped helical spring can be categorized as being a biased locking means requiring greater torque to disassemble than for assembly.